The present invention relates to a binocular. More particularly, the invention relates to a binocular with automatic focusing function.
Such binoculars with automatic focusing function have been proposed in Japanese published Patent Application No. S62-6205, Japanese published Patent Application No. S60-46407 and Japanese laid-open Patent Application No. S56-154705. In the binoculars disclosed in these prior art references, an object distance detection module is provided between a pair of object lenses positioned on both sides of the binocular, and a pair of light admitting windows for receiving light from an object and for sending it to the module is arranged at the outside of the object lens.
For this structure, the optical path arrangement for leading light from the light admitting window to the module is complicated, and the entire body cannot be made compact since the light admitting window is arranged at the outside of object lens.
In the above prior art, two light admitting windows are provided since they are required at the outsides of a pair of object lens. If the body is made compact by removing one of the light admitting windows, a problem arises in that the focus detection area changes according to the distance from an object as shown in FIG. 1A. That is, when the light sensing unit of focus sensor SA is arranged at the outside of one object lens OL as shown in FIG. 1A, though the focus detection area is A1' in FIG. 1B when the image scene is at A1, it is shifted to A2' in FIG. 1B when the image scene is at A2.
Further, the binocular according to the above prior art is disadvantageous in their great thickness (especially, at side edges) and their inferior external shapes since the occupation length from top to bottom of the light admitting window is greater than that of the object lenses.